Metal building end wall rafter to column

[qu88]

I am a new on metal building design and want to know followings:
1. The rafter is often connected to top of column.
2. The purlin is rigidly connected to rafter.
3. How will the concentrated load on top be transferred to roof diaphragm? by rotation of rafter? how to check the strength of rafter?

 

[BAretired]

I don't understand your question. Can you provide a sketch?

BA

 

[jayrod12]

Usually the wind columns have a diagonal brace where they connect to the rafter(beam) to the roof purlin. The purlins are not rigidly connected, usually just screws, would be considered pinned.

 

[phamENG]

Are we talking pre-engineered metal building, or metal buildings in general? If PEMBs, roof diaphragms are rare for small to medium sized buildings. They typically use discreet braces within the roof, except on very large or "one-off" buildings (which are hardly PEMBs anymore).

 

[hokie66]

My way, not necessarily how a lot of PEMB buildings are built:

The end wall wind beams/columns are connected to the rafters, but whether the connection is rigid or sliding depends on whether the columns support the rafters, or whether the rafter is just part of another rigid frame.

In either case, the purlins are not usually required to serve as struts/ties in the roof structure, but rather there is a truss in the roof plane. There should be a strut or truss node at the wind column connection.

The roofing should not be relied on as a diaphragm, as its purpose is to shed water.

 

[r13]

hokie66 is correct, the wind on the end wall shall be resisted by structural framing system, not by the roof deck.

 

[BAretired]

I still don't quite get the picture. I don't remember any steel building where the end wall was connected to rafters. Usually, if the roof is sloped, the fall line is parallel with the end wall. And I don't recall when I have seen purlins connected to rafters.

The OP should provide a sketch of the condition he is addressing. Otherwise, he is apt to get some strange answers.

BA

 

[hokie66]

Not sure why you need a picture of that, BA. The end wall has to be braced by the roof structure, so the wind beams/columns are connected to the rafters. In some cases the rafter is part of a rigid frame, in others it is just a beam between the wind columns. Therefore there are different type connections. Purlins not connected to rafters? How else would they be supported? The typical connection is a cleat welded to the rafter, with 2 bolts purlin to cleat.

 

[BAretired]

Okay Hokie66, I see it now and I also see the OP's concern about overturning of the beam. The one below looks a bit flimsy. I suppose a knee brace is contemplated from the column to a purlin.

BA

 

[hokie66]

That does look flimsy. And I can't see any purlin cleats, any brackets for wind bracing, or any cleats for fly bracing. Looks like the sides of that structure will be mostly open.

I would also be concerned with erection stability. Too many of these fall over like a pack of cards during construction. Those guys in the picture are living perilously.